1. Field of the Invention
The present invention relates to a variable magnification optical system. More particularly, the present invention relates to a variable magnification optical system (especially a compact zoom lens system that offers high magnification variation) suitable for, for example, a digital camera and a digital appliance equipped with an image capturing capability that capture an image of a subject with an image sensor, and to an image-taking apparatus provided therewith.
2. Description of Related Art
Due to recent widespread use of digital cameras, silver salt cameras seem to have been replaced with these digital cameras. Following the widespread use of digital cameras, there has been a demand for an even more compact digital camera and also a demand for an even more compact image-taking lens system. In response to such a demand, there has been introduced into the market a digital camera whose camera thickness is greatly reduced by using in an image-taking lens system a bending optical element, such as a prism, mirror, or the like, which bends an optical path. The feature of the digital camera of this type, which is not possessed by a sliver salt camera, is effectively utilized to achieve the slimming down of the digital camera. More specifically, the digital camera has a high degree of freedom in its arrangement of an image sensor (for example, a photoelectric converting element) in the camera. This digital camera also permits an image inverted in the image-taking lens system to be easily restored through electrical processing. Therefore, bending an optical path by the bending optical element is a method of reducing the camera thickness, which method is particularly achieved by the digital camera.
Patent documents 1 to 9 and the like disclose zoom lens systems each having a bending optical element provided for the purpose of reducing the camera thickness. The zoom lens systems disclosed in patent documents 1 to 3 each have a bending optical element arranged in a first lens unit. The zoom lens system disclosed in patent document 4 has a bending optical element arranged in a second lens unit. The zoom lens systems disclosed in patent documents 5 and 6 each have a bending optical element arranged between a second lens unit and a third lens unit. The zoom lens system disclosed in the seventh embodiment has a bending optical element in a third lens unit. The zoom lens systems disclosed in the eighth and ninth embodiments each have a bending optical element between a third lens unit and a fourth lens unit.                [Patent document 1] Japanese Patent Application Laid-open No. H8-248318        [Patent document 2] Japanese Patent Application Laid-open No. H9-138347        [Patent document 3] Japanese Patent Application Laid-open No. 2003-202500        [Patent document 4] Japanese Patent Application Laid-open No. 2004-102089        [Patent document 5] Japanese Patent Application Laid-open No. 2000-187159        [Patent document 6] Japanese Patent Application Laid-open No. 2000-187160        [Patent document 7] Japanese Patent Application Laid-open No. 2002-169088        [Patent document 8] Japanese Patent Application Laid-open No. H7-168096        [Patent document 9] Japanese Patent Application Laid-open No. H10-20191        
With an image sensor for use in a digital camera, the number of pixels has been increasing due to finer pixel pitch. Therefore, an image-taking lens system is demanded to have a high optical performance to catch up with the increase in the number of pixels in the image sensor. At the same time, the image-taking lens system is demanded to have a higher magnification variation ratio. However, it id difficult to ensure an optical performance to satisfy such high-standard specifications. Thus, aiming at ensuring a high optical performance inevitably results in upsizing of the image-taking lens system. Therefore, it is difficult for the conventional zoom lens systems disclosed in patent documents 1 to 9 to simultaneously meet mutually contradicting demands for higher magnification variation, a higher performance, and a more compact size.